1. Field of the Invention
The present invention relates to a chemical mechanical polishing (CMP) apparatus for polishing a semiconductor substrate. More specifically, the present invention relates to a polishing pad of the of the CMP apparatus.
2. Description of the Related Art
Recently, the rapid development of data processing and communications technologies has led to the demand for semiconductor devices, such as Dynamic Random Access Memories (DRAMs), that operate rapidly and have large storage capacities. Accordingly, semiconductor device fabrication technology has been developed with the aim of enhancing the integration, reliability, and response speed of semiconductor devices.
Fabricating semiconductor devices that have higher degrees of integration, are more miniaturized, and have large numbers of metal-bearing layers creates larger and larger steps on the surface of the substrates on which the semiconductor devices are formed. Techniques for planarizing the stepped surface of a semiconductor substrate include SOG (Spin On Glass), etch back, and reflow processes. However, chemical mechanical polishing (CMP) has been widely used for globally planarizing a semiconductor substrate surface. Chemical mechanical polishing is carried out by a CMP apparatus using a polishing pad.
FIG. 1 illustrates a conventional polishing pad of a CMP apparatus. Referring to FIG. 1, an upper surface of the conventional polishing pad is formed with grooves 1 and slurry holes 3. A polishing slurry is supplied onto an object to be polished (e.g., a semiconductor substrate) via the slurry holes 3. The slurry is dispersed via the grooves 1. In addition, the polishing pad is rotated during the CMP process. Thus, the slurry is spun off of the peripheral edge of the polishing pad due to the centrifugal force caused by the rotation of the polishing pad during the CMP process. For this reason, the slurry is distributed non-uniformly across the surface of the polishing pad.
Such non-uniform slurry distribution causes variations in the rate at which material is removed across the surface of the semiconductor substrate. In particular, the rate at which material is removed by the polishing process at the center of the semiconductor substrate is remarkably different from the rate at which material is removed at the periphery of the semiconductor substrate. The planarity of the semiconductor substrate depends on the uniformity of the removal rate. Thus, the conventional polishing pad makes it difficult to planarize a semiconductor substrate sufficiently and to effect a CMP process that is reproducible.